Caching time series data

ABSTRACT

A time series database system receives a request from a user device for first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in a persistent storage. The system determines whether all of the first time series data is stored in a memory. The system retrieves the second time series data from the persistent storage if all of the first time series data is not stored in the memory. The system stores the second time series data, excluding any part of the second time series data associated with a current time period, into the memory. The system causes the first time series data, being a subset of the second time series data retrieved from the persistent storage, to be outputted to the user device.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND

The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.

Time series data is a sequence of data points, typically consisting of successive measurements made over a time interval. Examples of time series data are ocean tides, counts of sunspots, and the daily closing value of the Dow Jones Industrial Average. Time series data is frequently plotted via line charts. Many domains of applied science and engineering which involve temporal measurements use time series data. Time series data analysis comprises methods for analyzing time series data in order to extract meaningful statistics and other characteristics of the data. Time series data forecasting is the use of a model to predict future values based on previously observed values. A time series database is a computer system that is optimized for handling time series data. In some fields, time series data is called a profile, a curve, or a trace. Despite the disparate names, many of the same mathematical operations, queries, or database transactions are useful for analyzing each of these time series data types. The implementation of a computerized database system that can correctly, reliably, and efficiently implement these operations must be specialized for time series data.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings like reference numbers are used to refer to like elements. Although the following figures depict various examples, the one or more implementations are not limited to the examples depicted in the figures.

FIG. 1 is an operational flow diagram illustrating a high level overview of a method for caching time series data, in an embodiment;

FIG. 2 illustrates a block diagram of an example of an environment wherein an on-demand database service might be used; and

FIG. 3 illustrates a block diagram of an embodiment of elements of FIG. 2 and various possible interconnections between these elements.

DETAILED DESCRIPTION General Overview

Retrieving time series data can take a long time, such as minutes, if the requested time series data spans a relatively large period of time, such as greater than a day, or has a large number of tags, such as time series data that is tagged as from multiple sources. This long retrieval time is due to a time series database system typically having to retrieve such data from persistent storage, such as a disk which is relatively slow.

In accordance with embodiments described herein, there are provided methods and systems for caching time series data. A time series database system receives a request from a user device for first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in a persistent storage. The time series database system determines whether all of the first time series data is stored in a memory. The time series database system retrieves the second time series data from the persistent storage if all of the first time series data is not stored in the memory. The time series database system stores the second time series data, excluding any part of the second time series data that is associated with a current time period, into the memory. The time series database system causes the first time series data to be outputted to the user device, the outputted first time series data being a subset of the second time series data retrieved from the persistent storage.

For example, the time series database system receives a request for the time series data metric computer X's CPU utilization from 5:00 P.M. on April 13^(th) to 4:45 P.M., the current time, on April 15^(th), and the time series database system's disk stores all of computer X's CPU utilization for many days, including April 13^(th) through the 15^(th). The time series database system determines whether all of this computer X CPU utilization data is stored in the time series database system's cache. The time series database system retrieves the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 4:45 P.M. on April 15^(th) from the disk because none of the computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:45 P.M. on April 15^(th) is stored in the cache. The time series database system stores the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 4:00 P.M. on April 15^(th) into the time series database system's cache. The time series database system outputs the requested computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:45 P.M. on April 15^(th) in response to the request.

In addition to retrieving and caching the user-requested data, the time series database system also retrieves and caches the unrequested computer X CPU utilization data for April 13^(th), in anticipation of the user also requesting this additional data, which the time series database system would be able to retrieve quickly from the cache rather than slowly from the disk. The time series database system does not cache the computer X CPU utilization data from 4:00 P.M. to 4:45 P.M. on April 15^(th) because this specific data will be supplemented by the computer X CPU utilization data from 4:45 P.M. to 5:00 P.M. within the current hour. Consequently, any subsequent requests for this small amount of specific data, along with the small amount of supplemental data, can be quickly retrieved via a short access of the disk.

Systems and methods are provided for caching time series data. As used herein, the term multi-tenant database system refers to those systems in which various elements of hardware and software of the database system may be shared by one or more customers. For example, a given application server may simultaneously process requests for a great number of customers, and a given database table may store rows for a potentially much greater number of customers. As used herein, the term query plan refers to a set of steps used to access information in a database system. Next, methods and mechanisms for caching time series data will be described with reference to example embodiments. The following detailed description will first describe a method for caching time series data.

While one or more implementations and techniques are described with reference to an embodiment in which caching time series data is implemented in a system having an application server providing a front end for an on-demand database service capable of supporting multiple tenants, the one or more implementations and techniques are not limited to multi-tenant databases nor deployment on application servers. Embodiments may be practiced using other database architectures, i.e., ORACLE®, DB2® by IBM and the like without departing from the scope of the embodiments claimed.

Any of the embodiments described herein may be used alone or together with one another in any combination. The one or more implementations encompassed within this specification may also include embodiments that are only partially mentioned or alluded to or are not mentioned or alluded to at all in this brief summary or in the abstract. Although various embodiments may have been motivated by various deficiencies with the prior art, which may be discussed or alluded to in one or more places in the specification, the embodiments do not necessarily address any of these deficiencies. In other words, different embodiments may address different deficiencies that may be discussed in the specification. Some embodiments may only partially address some deficiencies or just one deficiency that may be discussed in the specification, and some embodiments may not address any of these deficiencies.

FIG. 1 is an operational flow diagram illustrating a high level overview of a method 100 for caching time series data. A time series database system receives a request from a user device for a first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in persistent storage, block 102. For example and without limitation, this can include the time series database system receiving a request for the time series data metric computer X's CPU utilization from 5:00 P.M. on April 13^(th) to 4:45 P.M., the current time, on April 15^(th), and the time series database system's disk stores all of computer X's CPU utilization for many days, including April 13^(th) through the 15^(th). In another example, the time series database system receives a request for computer Y's free memory data from 9:00 A.M. on April 13^(th) to 5:00 P.M. on April 14^(th). Although these examples describe a request for time series data within a time range that spans multiple days that is tagged with only a single source, computer X, the request may be for time series data within a time range that spans less than one day and is tagged with multiple sources, or time series data within a time range that spans multiple days and is tagged with multiple sources, such as CPU utilizations for computer X, computer Y, and computer Z.

Having received the request, the time series database system determines whether all of the requested time series data is stored in memory, block 104. By way of example and without limitation, this can include the time series database system determining whether all of this computer X CPU utilization data is stored in the time series database system's cache. If all of the requested time series data is stored in the memory, the method 100 continues to block 106 to retrieve this requested data from the memory. If all of the requested time series data is not stored in the memory, the method 100 continues to block 110 to determine whether part of this requested data is in the memory.

If all of the requested time series data is stored in the memory, the time series database system optionally retrieves all of the time series data from the memory, block 106. In embodiments, this can include the time series database system retrieving all of the user-requested computer Y free memory data from 9:00 A.M. on April 13^(th) to 5:00 P.M. on April 14^(th) from the cache that stores all of this computer Y free memory data. The time series database system may retrieve the user-requested data from the memory by reading the data from memory key rows that contain one day's worth of the data.

After retrieving all of the requested time series data from memory, the time series database system optionally causes the time series data retrieved from memory to be outputted to the user device, block 108. For example and without limitation, this can include the time series database system outputting all of the requested computer Y free memory data, which was retrieved from cache, as a response to the user's request. Then the method 100 terminates.

Having determined that all of the requested time series data is not stored in memory, the time series database system optionally determines whether part of the requested time series data is stored in memory, block 110. By way of example and without limitation, this can include the time series database system determining whether part of the requested computer X CPU utilization data is stored in cache. If part of the requested time series data is stored in memory, the method 100 continues to block 112 to retrieve this part of the requested data. If no part of the requested time series data is stored in memory, the method 100 continues to block 114 to retrieve time series data from persistent storage.

If part of the requested time series data is stored in memory, the time series database system optionally retrieves the part of the requested time series data that is stored in memory, block 112. In embodiments, this can include the time series database system retrieving the computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:00 P.M. on April 15^(th) that is stored in cache. Since time series data that is associated with a current time period, such as the most recent hour, is not stored in the memory, the time series database system modifies any requests for time series data that is associated with a current time period to retrieve such time series data from the persistent storage. For example, the time series database system modifies the request to retrieve the computer X CPU utilization data from 4:00 P.M. to 4:45 P.M., the current time, on April 15^(th) from the disk.

If at least some of the requested time series data is not stored in memory, the time series database system retrieves time series data from the persistent storage, block 114. For example and without limitation, this can include the time series database system retrieving the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 4:45 P.M. on April 15^(th) from the disk because none of the computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:45 P.M. on April 15^(th) is stored in the time series database system's cache. In addition to retrieving the user-requested data, the time series database system also retrieves the unrequested computer X CPU utilization data for April 13^(th), in anticipation of the user also requesting this additional data.

The time range for the data retrieved from the persistent storage is based on the requested time range and a time period boundary that precedes the requested time range. For example, the time range for the computer X CPU utilization data retrieved from the disk is based on the request's initial time of 5:00 P.M. on April 13^(th), and adjusted to the initial recorded time for the request's initial day, 12:00 A.M. on April 13^(th). Although this example describes a time range for the data retrieved from persistent storage that is based on a time period boundary that precedes the requested time range, the time range for the data retrieved persistent storage may be based on a first time period boundary that precedes the requested time range and/or a second time period boundary that follows the requested time range. For example, in response to a request for computer X CPU utilization data from 11:00 P.M. on April 13^(th) to 1:00 A.M. on April 14^(th), the time range for the data retrieved from the persistent storage may be from 12:00 A.M. on April 13^(th) to 11:59 P.M. on April 14^(th), such that the time series database system retrieves 23 hours of computer X CPU utilization data that precedes the requested computer X CPU utilization data and 23 hours of computer X CPU utilization data that follows the requested computer X CPU utilization data. Similar to caching data that precedes the requested data, the time series database system may also cache data that follows the requested data in anticipation of the user requesting the following data. Although these examples describe time period boundaries based on day changes that precedes and/or follows the requested time range, the time period boundary used for adjusting the requested time period may be any time period boundary, such as an hour, half a day, or a week. The time series database system may convert the tags in the request to a tag set for the time series data because the tags in the request can contain Booleans or conditions, which should be converted to a single tag set for a time series data.

Having retrieved time series data from persistent storage, the time series database system stores the time series data retrieved from the persistent storage, excluding any part of the time series data retrieved from persistent storage that is associated with a current time period, into memory, block 116. By way of example and without limitation, this can include the time series database system storing the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 4:00 P.M. on April 15^(th) into the time series database system's cache, and adding both the time series data metric and a new cache key as entries for the cache. In addition to caching the user-requested data, the time series database system also caches the unrequested computer X CPU utilization data for April 13^(th), in anticipation of the user also requesting this additional data, which the time series database system would be able to retrieve quickly from the cache rather than slowly from the disk. The time series database system does not cache the computer X CPU utilization data from 4:00 P.M. to 4:45 P.M. on April 15^(th) because this specific data will be supplemented by the computer X CPU utilization data from 4:45 P.M. to 5:00 P.M. within the current hour. Caching the computer X CPU utilization data from 4:00 P.M. to 4:45 P.M. on April 15^(th) would be inefficient because this same data would be retrieved from the disk when the computer X CPU utilization data from 4:45 P.M. to 5:00 P.M. is retrieved based on the key used for storing the computer X CPU utilization data from 4:00 P.M. to 5:00 P.M. Consequently, any subsequent requests for this small amount of specific data, along with the small amount of supplemental data, can be quickly retrieved via a short access of the disk.

Although this example describes the current time period as the current hour, the current time period for which the requested time series data is not stored in memory may be any current time period, such as the current minute, the current half-hour, or the current day. The time series database system may store the time series data retrieved from the persistent storage into memory by fracturing the time series data retrieved from the persistent storage based on time period boundaries corresponding to each memory key. For example, the time series database system caches the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 4:00 P.M. on April 15^(th) by caching the computer X CPU utilization data from 12:00 A.M. on April 13^(th) to 11:59 P.M. on April 13^(th) with an April 13^(th) cache key, caching the computer X CPU utilization data from 12:00 A.M. on April 14^(th) to 11:59 P.M. on April 14^(th) with an April 14^(th) cache key, and caching the computer X CPU utilization data from 12:00 A.M. on April 15^(th) to 4:00 P.M. on April 15^(th) with an April 15^(th) cache key. Although these examples describe caching based on day changes that precede and/or follow the requested time range, the caching may be based on any time period boundary, such as an hour, half a day, or a week. The time series database system may use a day as a time period boundary because caching based on such a time period boundary would result in requests for time series data that spans a long time searching fewer key spaces. If the tags specified in the request differ from the tags specified in the data retrieved from memory and/or the data retrieved from the persistent storage, then the time series database system adds the tags specified in the request as one memory key and adds the tags retrieved from memory and/or the tags retrieved from the persistent storage as another memory key, such that a subsequent request for either set of tags would result in a “cache hit.” The time series database system writes raw time series data to persistent storage, not to memory, because memory stores transformed data that is retrieved from the persistent storage.

After caching at least some of the time series data retrieved from the persistent storage, the time series database system causes the requested time series data to be outputted to the user device, the outputted time series data being a subset of the time series data retrieved from the persistent storage, block 118. In embodiments, this can include the time series database system trimming the retrieved computer X CPU utilization data to output the requested computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:45 P.M. on April 15^(th) in response to the request. If the response to the request includes both data retrieved from memory and data retrieved from the persistent storage, then the time series database system maps the tags retrieved from memory to the tags retrieved from the persistent storage.

Having output the response to the request, the time series database system optionally stores third time series data associated with the time series data retrieved from persistent storage and associated with the current time period into memory in response to the expiration of the current time period, block 120. For example and without limitation, this can include the time series database system caching the computer X CPU utilization data from 4:00 P.M. on April 15^(th) to 4:59 P.M. on April 15^(th) when the current hour expires at 5:00 P.M. on April 15^(th), since the computer X CPU utilization data from 4:00 P.M. to 4:45 P.M. on April 15^(th) was not cached. The time series database system continues caching the time series data associated with each current time period following the expiration of each current time period, until the time series data is subsequently evicted from memory. For example, at 6:00 P.M. the time series database system caches the computer X CPU utilization data from 5:00 P.M. to 5:59 P.M. on April 15^(th), at 7:00 P.M. the time series database system caches the computer X CPU utilization data from 6:00 P.M. to 6:59 P.M. on April 15^(th), etc., which insures that the cached computer X CPU utilization data stays current up to the most recent hour. When the caching of the time series data associated with the time series data retrieved from persistent storage and the current time period reaches a time period boundary, the time series database system creates a new memory key based on the time period boundary, and begins caching based on the new memory key. For example, after the time series database system cached the computer X CPU utilization data from 11:00 P.M. to 11:59 P.M. on April 15^(th), the time series database system creates a new cache key for computer X CPU utilization data on April 16^(th), and caches the computer X CPU utilization data from 12:00 A.M. to 12:59 A.M. on April 16^(th) at 1:00 A.M. on April 16^(th).

After storing the data associated with the current time period in memory, the time series database system optionally evicts the time series data retrieved from persistent storage memory based on a request time and/or a request frequency associated with the time series data retrieved from persistent storage, block 122. By way of example and without limitation, this can include the time series database system evicting the computer X CPU utilization data from 5:00 P.M. on April 13^(th) to 4:00 P.M. on April 18^(th) from cache because no user has requested any of this data for 3 days since the single request for part of this data on April 15^(th). The eviction of the cached time series data may be based on an expiry time specified in a cache key.

The method 100 may be repeated as desired. Although this disclosure describes the blocks 102-122 executing in a particular order, the blocks 102-122 may be executed in a different order. In other implementations, each of the blocks 102-122 may also be executed in combination with other blocks and/or some blocks may be divided into a different set of blocks.

System Overview

FIG. 2 illustrates a block diagram of an environment 210 wherein an on-demand database service might be used. The environment 210 may include user systems 212, a network 214, a system 216, a processor system 217, an application platform 218, a network interface 220, a tenant data storage 222, a system data storage 224, program code 226, and a process space 228. In other embodiments, the environment 210 may not have all of the components listed and/or may have other elements instead of, or in addition to, those listed above.

The environment 210 is an environment in which an on-demand database service exists. A user system 212 may be any machine or system that is used by a user to access a database user system. For example, any of the user systems 212 may be a handheld computing device, a mobile phone, a laptop computer, a work station, and/or a network of computing devices. As illustrated in FIG. 2 (and in more detail in FIG. 3) the user systems 212 might interact via the network 214 with an on-demand database service, which is the system 216.

An on-demand database service, such as the system 216, is a database system that is made available to outside users that do not need to necessarily be concerned with building and/or maintaining the database system, but instead may be available for their use when the users need the database system (e.g., on the demand of the users). Some on-demand database services may store information from one or more tenants stored into tables of a common database image to form a multi-tenant database system (MTS). Accordingly, the “on-demand database service 216” and the “system 216” will be used interchangeably herein. A database image may include one or more database objects. A relational database management system (RDMS) or the equivalent may execute storage and retrieval of information against the database object(s). The application platform 218 may be a framework that allows the applications of the system 216 to run, such as the hardware and/or software, e.g., the operating system. In an embodiment, the on-demand database service 216 may include the application platform 218 which enables creation, managing and executing one or more applications developed by the provider of the on-demand database service, users accessing the on-demand database service via user systems 212, or third party application developers accessing the on-demand database service via the user systems 212.

The users of the user systems 212 may differ in their respective capacities, and the capacity of a particular user system 212 might be entirely determined by permissions (permission levels) for the current user. For example, where a salesperson is using a particular user system 212 to interact with the system 216, that user system 212 has the capacities allotted to that salesperson. However, while an administrator is using that user system 212 to interact with the system 216, that user system 212 has the capacities allotted to that administrator. In systems with a hierarchical role model, users at one permission level may have access to applications, data, and database information accessible by a lower permission level user, but may not have access to certain applications, database information, and data accessible by a user at a higher permission level. Thus, different users will have different capabilities with regard to accessing and modifying application and database information, depending on a user's security or permission level.

The network 214 is any network or combination of networks of devices that communicate with one another. For example, the network 214 may be any one or any combination of a LAN (local area network), WAN (wide area network), telephone network, wireless network, point-to-point network, star network, token ring network, hub network, or other appropriate configuration. As the most common type of computer network in current use is a TCP/IP (Transfer Control Protocol and Internet Protocol) network, such as the global internetwork of networks often referred to as the “Internet” with a capital “I,” that network will be used in many of the examples herein. However, it should be understood that the networks that the one or more implementations might use are not so limited, although TCP/IP is a frequently implemented protocol.

The user systems 212 might communicate with the system 216 using TCP/IP and, at a higher network level, use other common Internet protocols to communicate, such as HTTP, FTP, AFS, WAP, etc. In an example where HTTP is used, the user systems 212 might include an HTTP client commonly referred to as a “browser” for sending and receiving HTTP messages to and from an HTTP server at the system 216. Such an HTTP server might be implemented as the sole network interface between the system 216 and the network 214, but other techniques might be used as well or instead. In some implementations, the interface between the system 216 and the network 214 includes load sharing functionality, such as round-robin HTTP request distributors to balance loads and distribute incoming HTTP requests evenly over a plurality of servers. At least as for the users that are accessing that server, each of the plurality of servers has access to the MTS' data; however, other alternative configurations may be used instead.

In one embodiment, the system 216, shown in FIG. 2, implements a web-based customer relationship management (CRM) system. For example, in one embodiment, the system 216 includes application servers configured to implement and execute CRM software applications as well as provide related data, code, forms, webpages and other information to and from the user systems 212 and to store to, and retrieve from, a database system related data, objects, and Webpage content. With a multi-tenant system, data for multiple tenants may be stored in the same physical database object, however, tenant data typically is arranged so that data of one tenant is kept logically separate from that of other tenants so that one tenant does not have access to another tenant's data, unless such data is expressly shared. In certain embodiments, the system 216 implements applications other than, or in addition to, a CRM application. For example, the system 216 may provide tenant access to multiple hosted (standard and custom) applications, including a CRM application. User (or third party developer) applications, which may or may not include CRM, may be supported by the application platform 218, which manages creation, storage of the applications into one or more database objects and executing of the applications in a virtual machine in the process space of the system 216.

One arrangement for elements of the system 216 is shown in FIG. 2, including the network interface 220, the application platform 218, the tenant data storage 222 for tenant data 223, the system data storage 224 for system data 225 accessible to the system 216 and possibly multiple tenants, the program code 226 for implementing various functions of the system 216, and the process space 228 for executing MTS system processes and tenant-specific processes, such as running applications as part of an application hosting service. Additional processes that may execute on the system 216 include database indexing processes.

Several elements in the system shown in FIG. 2 include conventional, well-known elements that are explained only briefly here. For example, each of the user systems 212 could include a desktop personal computer, workstation, laptop, PDA, cell phone, or any wireless access protocol (WAP) enabled device or any other computing device capable of interfacing directly or indirectly to the Internet or other network connection. Each of the user systems 212 typically runs an HTTP client, e.g., a browsing program, such as Microsoft's Internet Explorer browser, Netscape's Navigator browser, Opera's browser, or a WAP-enabled browser in the case of a cell phone, PDA or other wireless device, or the like, allowing a user (e.g., subscriber of the multi-tenant database system) of the user systems 212 to access, process and view information, pages and applications available to it from the system 216 over the network 214. Each of the user systems 212 also typically includes one or more user interface devices, such as a keyboard, a mouse, trackball, touch pad, touch screen, pen or the like, for interacting with a graphical user interface (GUI) provided by the browser on a display (e.g., a monitor screen, LCD display, etc.) in conjunction with pages, forms, applications and other information provided by the system 216 or other systems or servers. For example, the user interface device may be used to access data and applications hosted by the system 216, and to perform searches on stored data, and otherwise allow a user to interact with various GUI pages that may be presented to a user. As discussed above, embodiments are suitable for use with the Internet, which refers to a specific global internetwork of networks. However, it should be understood that other networks can be used instead of the Internet, such as an intranet, an extranet, a virtual private network (VPN), a non-TCP/IP based network, any LAN or WAN or the like.

According to one embodiment, each of the user systems 212 and all of its components are operator configurable using applications, such as a browser, including computer code run using a central processing unit such as an Intel Pentium® processor or the like. Similarly, the system 216 (and additional instances of an MTS, where more than one is present) and all of their components might be operator configurable using application(s) including computer code to run using a central processing unit such as the processor system 217, which may include an Intel Pentium® processor or the like, and/or multiple processor units. A computer program product embodiment includes a machine-readable storage medium (media) having instructions stored thereon/in which can be used to program a computer to perform any of the processes of the embodiments described herein. Computer code for operating and configuring the system 216 to intercommunicate and to process webpages, applications and other data and media content as described herein are preferably downloaded and stored on a hard disk, but the entire program code, or portions thereof, may also be stored in any other volatile or non-volatile memory medium or device as is well known, such as a ROM or RAM, or provided on any media capable of storing program code, such as any type of rotating media including floppy disks, optical discs, digital versatile disk (DVD), compact disk (CD), microdrive, and magneto-optical disks, and magnetic or optical cards, nanosystems (including molecular memory ICs), or any type of media or device suitable for storing instructions and/or data. Additionally, the entire program code, or portions thereof, may be transmitted and downloaded from a software source over a transmission medium, e.g., over the Internet, or from another server, as is well known, or transmitted over any other conventional network connection as is well known (e.g., extranet, VPN, LAN, etc.) using any communication medium and protocols (e.g., TCP/IP, HTTP, HTTPS, Ethernet, etc.) as are well known. It will also be appreciated that computer code for implementing embodiments can be implemented in any programming language that can be executed on a client system and/or server or server system such as, for example, C, C++, HTML, any other markup language, Java™, JavaScript, ActiveX, any other scripting language, such as VBScript, and many other programming languages as are well known may be used. (Java™ is a trademark of Sun Microsystems, Inc.).

According to one embodiment, the system 216 is configured to provide webpages, forms, applications, data and media content to the user (client) systems 212 to support the access by the user systems 212 as tenants of the system 216. As such, the system 216 provides security mechanisms to keep each tenant's data separate unless the data is shared. If more than one MTS is used, they may be located in close proximity to one another (e.g., in a server farm located in a single building or campus), or they may be distributed at locations remote from one another (e.g., one or more servers located in city A and one or more servers located in city B). As used herein, each MTS could include one or more logically and/or physically connected servers distributed locally or across one or more geographic locations. Additionally, the term “server” is meant to include a computer system, including processing hardware and process space(s), and an associated storage system and database application (e.g., OODBMS or RDBMS) as is well known in the art. It should also be understood that “server system” and “server” are often used interchangeably herein. Similarly, the database object described herein can be implemented as single databases, a distributed database, a collection of distributed databases, a database with redundant online or offline backups or other redundancies, etc., and might include a distributed database or storage network and associated processing intelligence.

FIG. 3 also illustrates the environment 210. However, in FIG. 3 elements of the system 216 and various interconnections in an embodiment are further illustrated. FIG. 3 shows that the each of the user systems 212 may include a processor system 212A, a memory system 212B, an input system 212C, and an output system 212D. FIG. 3 shows the network 214 and the system 216. FIG. 3 also shows that the system 216 may include the tenant data storage 222, the tenant data 223, the system data storage 224, the system data 225, a User Interface (UI) 330, an Application Program Interface (API) 332, a PL/SOQL 334, save routines 336, an application setup mechanism 338, applications servers 300 ₁-300 _(N), a system process space 302, tenant process spaces 304, a tenant management process space 310, a tenant storage area 312, a user storage 314, and application metadata 316. In other embodiments, the environment 210 may not have the same elements as those listed above and/or may have other elements instead of, or in addition to, those listed above.

The user systems 212, the network 214, the system 216, the tenant data storage 222, and the system data storage 224 were discussed above in reference to FIG. 2. Regarding the user systems 212, the processor system 212A may be any combination of one or more processors. The memory system 212B may be any combination of one or more memory devices, short term, and/or long term memory. The input system 212C may be any combination of input devices, such as one or more keyboards, mice, trackballs, scanners, cameras, and/or interfaces to networks. The output system 212D may be any combination of output devices, such as one or more monitors, printers, and/or interfaces to networks. As shown by FIG. 3, the system 216 may include the network interface 220 (of FIG. 2) implemented as a set of HTTP application servers 300, the application platform 218, the tenant data storage 222, and the system data storage 224. Also shown is the system process space 302, including individual tenant process spaces 304 and the tenant management process space 310. Each application server 300 may be configured to access tenant data storage 222 and the tenant data 223 therein, and the system data storage 224 and the system data 225 therein to serve requests of the user systems 212. The tenant data 223 might be divided into individual tenant storage areas 312, which can be either a physical arrangement and/or a logical arrangement of data. Within each tenant storage area 312, the user storage 314 and the application metadata 316 might be similarly allocated for each user. For example, a copy of a user's most recently used (MRU) items might be stored to the user storage 314. Similarly, a copy of MRU items for an entire organization that is a tenant might be stored to the tenant storage area 312. The UI 330 provides a user interface and the API 332 provides an application programmer interface to the system 216 resident processes to users and/or developers at the user systems 212. The tenant data and the system data may be stored in various databases, such as one or more Oracle™ databases.

The application platform 218 includes the application setup mechanism 338 that supports application developers' creation and management of applications, which may be saved as metadata into the tenant data storage 222 by the save routines 336 for execution by subscribers as one or more tenant process spaces 304 managed by the tenant management process 310 for example. Invocations to such applications may be coded using the PL/SOQL 334 that provides a programming language style interface extension to the API 332. A detailed description of some PL/SOQL language embodiments is discussed in commonly owned U.S. Pat. No. 7,730,478 entitled, METHOD AND SYSTEM FOR ALLOWING ACCESS TO DEVELOPED APPLICATIONS VIA A MULTI-TENANT ON-DEMAND DATABASE SERVICE, by Craig Weissman, filed Sep. 21, 2007, which is incorporated in its entirety herein for all purposes. Invocations to applications may be detected by one or more system processes, which manages retrieving the application metadata 316 for the subscriber making the invocation and executing the metadata as an application in a virtual machine.

Each application server 300 may be communicably coupled to database systems, e.g., having access to the system data 225 and the tenant data 223, via a different network connection. For example, one application server 300 ₁ might be coupled via the network 214 (e.g., the Internet), another application server 300 _(N-1) might be coupled via a direct network link, and another application server 300 _(N) might be coupled by yet a different network connection. Transfer Control Protocol and Internet Protocol (TCP/IP) are typical protocols for communicating between application servers 300 and the database system. However, it will be apparent to one skilled in the art that other transport protocols may be used to optimize the system depending on the network interconnect used.

In certain embodiments, each application server 300 is configured to handle requests for any user associated with any organization that is a tenant. Because it is desirable to be able to add and remove application servers from the server pool at any time for any reason, there is preferably no server affinity for a user and/or organization to a specific application server 300. In one embodiment, therefore, an interface system implementing a load balancing function (e.g., an F5 Big-IP load balancer) is communicably coupled between the application servers 300 and the user systems 212 to distribute requests to the application servers 300. In one embodiment, the load balancer uses a least connections algorithm to route user requests to the application servers 300. Other examples of load balancing algorithms, such as round robin and observed response time, also can be used. For example, in certain embodiments, three consecutive requests from the same user could hit three different application servers 300, and three requests from different users could hit the same application server 300. In this manner, the system 216 is multi-tenant, wherein the system 216 handles storage of, and access to, different objects, data and applications across disparate users and organizations.

As an example of storage, one tenant might be a company that employs a sales force where each salesperson uses the system 216 to manage their sales process. Thus, a user might maintain contact data, leads data, customer follow-up data, performance data, goals and progress data, etc., all applicable to that user's personal sales process (e.g., in the tenant data storage 222). In an example of a MTS arrangement, since all of the data and the applications to access, view, modify, report, transmit, calculate, etc., can be maintained and accessed by a user system having nothing more than network access, the user can manage his or her sales efforts and cycles from any of many different user systems. For example, if a salesperson is visiting a customer and the customer has Internet access in their lobby, the salesperson can obtain critical updates as to that customer while waiting for the customer to arrive in the lobby.

While each user's data might be separate from other users' data regardless of the employers of each user, some data might be organization-wide data shared or accessible by a plurality of users or all of the users for a given organization that is a tenant. Thus, there might be some data structures managed by the system 216 that are allocated at the tenant level while other data structures might be managed at the user level. Because an MTS might support multiple tenants including possible competitors, the MTS should have security protocols that keep data, applications, and application use separate. Also, because many tenants may opt for access to an MTS rather than maintain their own system, redundancy, up-time, and backup are additional functions that may be implemented in the MTS. In addition to user-specific data and tenant specific data, the system 216 might also maintain system level data usable by multiple tenants or other data. Such system level data might include industry reports, news, postings, and the like that are sharable among tenants.

In certain embodiments, the user systems 212 (which may be client systems) communicate with the application servers 300 to request and update system-level and tenant-level data from the system 216 that may require sending one or more queries to the tenant data storage 222 and/or the system data storage 224. The system 216 (e.g., an application server 300 in the system 216) automatically generates one or more SQL statements (e.g., one or more SQL queries) that are designed to access the desired information. The system data storage 224 may generate query plans to access the requested data from the database.

Each database can generally be viewed as a collection of objects, such as a set of logical tables, containing data fitted into predefined categories. A “table” is one representation of a data object, and may be used herein to simplify the conceptual description of objects and custom objects. It should be understood that “table” and “object” may be used interchangeably herein. Each table generally contains one or more data categories logically arranged as columns or fields in a viewable schema. Each row or record of a table contains an instance of data for each category defined by the fields. For example, a CRM database may include a table that describes a customer with fields for basic contact information such as name, address, phone number, fax number, etc. Another table might describe a purchase order, including fields for information such as customer, product, sale price, date, etc. In some multi-tenant database systems, standard entity tables might be provided for use by all tenants. For CRM database applications, such standard entities might include tables for Account, Contact, Lead, and Opportunity data, each containing pre-defined fields. It should be understood that the word “entity” may also be used interchangeably herein with “object” and “table”.

In some multi-tenant database systems, tenants may be allowed to create and store custom objects, or they may be allowed to customize standard entities or objects, for example by creating custom fields for standard objects, including custom index fields. U.S. Pat. No. 7,779,039, filed Apr. 2, 2004, entitled “Custom Entities and Fields in a Multi-Tenant Database System”, which is hereby incorporated herein by reference, teaches systems and methods for creating custom objects as well as customizing standard objects in a multi-tenant database system. In certain embodiments, for example, all custom entity data rows are stored in a single multi-tenant physical table, which may contain multiple logical tables per organization. It is transparent to customers that their multiple “tables” are in fact stored in one large table or that their data may be stored in the same table as the data of other customers.

While one or more implementations have been described by way of example and in terms of the specific embodiments, it is to be understood that one or more implementations are not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A system for caching time series data, the system comprising: one or more processors; and a non-transitory computer readable medium storing a plurality of instructions, which when executed, cause the one or more processors to: receive, by a time series database system, a request from a user device for first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in a persistent storage; determine, by the time series database system, whether all of the first time series data is stored in a memory; retrieve, by the time series database system, when it is determined that all of the first time series data is not stored in the memory, the second time series data from the persistent storage; store, by the time series database system, into the memory, the second time series data, excluding any part of the second time series data that is associated with a current time period; and cause, by the time series database system, the first time series data to be outputted to the user device, the outputted first time series data being a subset of the second time series data retrieved from the persistent storage.
 2. The system of claim 1, comprising further instructions, which when executed, cause the one or more processors to: retrieve, by the time series database system, all of the first time series data from the memory in response to a determination that all of the first time series data is stored in the memory; and cause, by the time series database system, all of the first time series data retrieved from the memory to be outputted to the user device.
 3. The system of claim 1, comprising further instructions, which when executed, cause the one or more processors to: determine, by the time series database system, whether a part of the first time series data is stored in the memory in response to a determination that all of the first time series data is not stored in the memory; and retrieve, by the time series database system, the part of the first time series data that is stored in the memory in response to a determination that the part of the first time series data is stored in the memory.
 4. The system of claim 3, wherein the first time series data to be outputted to the user device comprises the part of the first time series data that is retrieved from the memory.
 5. The system of claim 1, wherein the second time range is based on the first time range and a time period boundary that precedes the first time range.
 6. The system of claim 1, comprising further instructions, which when executed, cause the one or more processors to store, by the time series database system, third time series data associated with the second time series data and associated with the current time period into the memory in response to an expiration of the current time period.
 7. The system of claim 1, comprising further instructions, which when executed, cause the one or more processors to evict, by the time series database system, at least a part of the second time series data from the memory based on at least one of a request time and a request frequency associated with the second time series data.
 8. A computer program product comprising computer-readable program code to be executed by one or more processors when retrieved from a non-transitory computer-readable medium, the program code including instructions to: receive, by a time series database system, a request from a user device for first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in a persistent storage; determine, by the time series database system, whether all of the first time series data is stored in a memory; retrieve, by the time series database system, when it is determined that all of the first time series data is not stored in the memory, the second time series data from the persistent storage; store, by the time series database system, into the memory, the second time series data, excluding any part of the corresponding time series data that is associated with a current time period; and cause, by the time series database system, the first time series data to be outputted to the user device, the outputted first time series data being a subset of the second time series data retrieved from the persistent storage.
 9. The computer program product of claim 8, wherein the program code comprises further instructions to: retrieve, by the time series database system, all of the first time series data from the memory in response to a determination that all of the first time series data is stored in the memory; and cause, by the time series database system, all of the first time series data retrieved from the memory to be outputted to the user device.
 10. The computer program product of claim 8, wherein the program code comprises further instructions to: determine, by the time series database system, whether a part of the first time series data is stored in the memory in response to a determination that all of the first time series data is not stored in the memory; and retrieve, by the time series database system, the part of the first time series data that is stored in the memory in response to a determination that the part of the first time series data is stored in the memory, wherein the first time series data outputted to the user device comprises the part of the first time series data that is retrieved from the memory.
 11. The computer program product of claim 8, wherein the second time range is based on the first time range and a time period boundary that precedes the first time range.
 12. The computer program product of claim 8, wherein the program code comprises further instructions to store, by the time series database system, third time series data associated with the second time series data and associated with the current time period into the memory in response to an expiration of the current time period.
 13. The computer program product of claim 8, wherein the program code comprises further instructions to evict, by the time series database system, at least a part of the second time series data from the memory based on at least one of a request time and a request frequency associated with the second time series data.
 14. A method comprising: receiving, by a time series database system, a request from a user device for first time series data within a first time range, the first time series data being a subset of second time series data within a second time range, the second time series data being stored in a persistent storage; determining, by the time series database system, whether all of the first time series data is stored in a memory; retrieving, by the time series database system, when it is determined that all of the first time series data is not stored in the memory, the second time series data from the persistent storage; storing, by the time series database system, into the memory, the second time series data, excluding any part of the second time series data that is associated with a current time period; and causing, by the time series database system, the first time series data to be outputted to the user device, the outputted first time series data being a subset of the second time series data retrieved from the persistent storage.
 15. The method of claim 14, wherein the method further comprises: retrieving, by the time series database system, all of the first time series data from the memory in response to a determination that all of the first time series data is stored in the memory; and causing, by the time series database system, all of the first time series data retrieved from the memory to be outputted to the user device.
 16. The method of claim 14, wherein the method further comprises: determining, by the time series database system, whether a part of the first time series data is stored in the memory in response to a determination that all of the first time series data is not stored in the memory; and retrieving, by the time series database system, the part of the first time series data that is stored in the memory in response to a determination that the part of the first time series data is stored in the memory.
 17. The method of claim 16, wherein the first time series data outputted to the user device comprises the part of the first time series data that is retrieved from the memory.
 18. The method of claim 14, wherein the second time range is based on the first time range and a time period boundary that precedes the first time range.
 19. The method of claim 14, wherein the method further comprises storing, by the time series database system, third time series data associated with the second time series data and associated with the current time period into the memory in response to an expiration of the current time period.
 20. The method of claim 14, wherein the method further comprises evicting, by the time series database system, at least a part of the second time series data from the memory based on at least one of a request time and a request frequency associated with the second time series data. 